1. Field of the Invention
The present invention relates to a method for driving a memory-type AC (Alternating Current) plasma display panel and particularly to the AC plasma display panel being capable of preventing deterioration of an image quality caused by erroneous discharge.
The present application claims priority of Japanese Patent Application No. 2001-328496 filed on Oct. 26, 2001, which is hereby incorporated by reference.
2. Description of the Related Art
FIG. 4 is a cross-sectional view showing a configuration of a conventional AC plasma display panel. In the AC plasma display panel, a front substrate 11 and a rear substrate 15 are provided both of which face each other. Both the front substrate 11 and the rear substrate 15 are constructed of an insulating substrate made of glass.
On the face of the front substrate 11 facing the rear substrate 15 is formed a plurality of pairs of surface discharging electrodes (not shown), each pair of which is made up of a scanning electrode 12a and a sustaining electrodes 12b being respectively made of an ITO (Indium Tin Oxide) film or a NESA glass film being used as a transparent electrode. Moreover, on each of the scanning electrodes 12a and the sustaining electrodes 12b is a bus electrode 13 made of a metal electrode used to lower a resistance value between the scanning electrodes 12a and the sustaining electrodes 12b and a driver (not shown).
As the bus electrode 13, in ordinary cases, there is used a thin multilayer electrode made up of a Cr (chromium) film, a Cu (copper) film, and a Cr film formed and stacked sequentially in this order or a thick film electrode made of Ag (silver). The scanning electrodes 12a, sustaining electrodes 12b, and bus electrodes 13 are coated with a dielectric layer 14. As a material for the dielectric layer 14, glass with a low melting point is used in ordinary cases. Moreover, on the dielectric layer 14 is formed a MgO (magnesium oxide) film (not shown) with a film thickness of 0.5 μm to 1 μm by using a method of vacuum deposition with the aim of preventing damage caused by an ion or an electron generated by discharging and of lowering discharging voltage.
On the other hand, on a face of the rear substrate 15 facing the front substrate 11 is formed a plurality of data electrodes 16 constructed of a thick film made of Ag which extends in a direction orthogonal to a direction in which the scanning electrodes 12a and sustaining the electrodes 12b extend. Moreover, a white dielectric layer 17 obtained by printing and then burning a glass paste being a mixture of a powder of a white oxide (such as aluminum oxide, titanium oxide, or a like) with a power of glass with a low melting point or a like is formed in a manner so as to cover the data electrode 16. The white dielectric layer 17 has a function of reflecting visible light fed from various kinds of fluorescent layers 18 each providing a different color and guiding the reflected light toward a side of the front substrate 11, thus enhancing an effect by the visible light. Moreover, on the white dielectric layer 17 is formed in a separate manner, by using thick film printing technology, various kinds of the fluorescent layers 18 which convert ultraviolet color produced by gas discharging to visible light.
Furthermore, the front substrate 11 faces the rear substrate 15 being apart from each other by an interval of 100 μm to 200 μm with partition walls (not shown) constructed of a grid-shaped or stripe-shaped insulating body being interposed between them and with a discharging cell 19 being sandwiched between them. Discharging gas composed of helium, neon, or xenon, or a mixed gas of these gases or a like is filled in a hermetic manner between the front substrate 11 and the rear substrate 15. Moreover, the partition walls (not shown) are formed by thick film forming technology using a mixture of aluminum oxide, magnesium oxide, titanium oxide, or a like with glass.
Next, discharging operations in the selected discharging cell 19, out of operations of the AC plasma display panel configured as above, are explained by referring to FIG. 5. FIG. 5 is a timing chart showing a conventional method for driving the AC plasma display panel.
One field required for displaying one screen is made up of a plurality of sub-fields and a sustaining erasing period, a pre-discharging period, a pre-discharging erasing period, a writing period, and a sustaining period are set for each sub-field.
First, during the sustaining erasing period, wall charges which occurred in a vicinity of the scanning electrodes 12a and the sustaining electrodes 12b during the sustaining period of the sub-field existed immediately before are erased by applying an erasing pulse Pe to the scanning electrodes 12a. 
Then, surface discharge is made to occur between the scanning electrodes 12a and the sustaining electrodes 12b by applying a pre-discharging pulse Pp to the scanning electrodes 12a and the sustaining electrodes 12b during the pre-discharging period.
Next, by applying an erasing pulse Pe to the scanning electrodes 12a during the pre-discharging erasing period, wall charges which occurred in a vicinity of the scanning electrodes 12a and the sustaining electrodes 12b during the pre-discharging period are erased.
During the writing period subsequent to the pre-discharging erasing period, by applying a writing pulse Pw so as to scan sequentially an entire screen of the scanning electrodes 12a and also by applying a data pulse Pd to the data electrodes 16 in accordance with desired display data in synchronization with the above application of the writing pulse Pw, discharging is made to occur selectively between the scanning electrodes 12a and the data electrodes 16.
During the sustaining period subsequent to the writing period, by applying a voltage pulse Psus to the scanning electrodes 12a and the sustaining electrodes 12b in which polarities of the voltage pulse Psus fed to the scanning electrodes 12a and sustaining electrodes 12b are opposite to each other, opposed discharge occurred during the writing period is maintained as surface discharge between the scanning electrodes 12a and sustaining electrodes 12b for displaying.
By employing the method described above, during the pre-discharging period and pre-discharging erasing period, since, after the occurrence of the surface discharge on an entire screen, feeble discharging occurs, wall charges existing on electrodes making up the discharging cell 19 are erased and space charges made up of charged particles can be left within the discharging cell 19. Therefore, during the writing period subsequent to these period described above, opposed discharge being made to occur between the scanning electrodes 12a and the data electrodes 16 in a manner to correspond to display data can be made to surely occur.
Also, during the writing period, discharging is made to occur between the scanning electrodes 12a and the data electrodes 16 and, as a result, positive wall charges are produced on the scanning electrodes 12a and negative wall charges are produced on the data electrodes 16. A voltage produced by these wall charges is superimposed on a voltage of the voltage pulse Psus applied to the scanning electrodes 12a and sustaining electrodes 12b during a subsequent sustaining period and, as a result, the superimposed voltage exceeds surface discharge initiating voltage in a pair of surface discharging electrodes and therefore discharging corresponding to display data is caused to occur and can be maintained. This enables a desired display pattern to be obtained.
Next, a method for achieving a gray-scale display by controlling discharging of the discharging cell 19 in accordance with the driving method described above is explained by referring to FIG. 6 and FIG. 7. FIG. 6 is a timing chart showing a relation between elapsed time and display since a start of operations of the AC plasma display panel according to the conventional method described above and FIG. 7 is a timing chart explaining configurations in one field.
Gray-scale display can be achieved by exerting control on a number of times of discharging during the sustaining period using the driving method explained above. For example, as shown in FIG. 6, one field (F) 4 required for displaying one screen is provided repeatedly 50 to 70 times per one second. As a result, by image retention produced by a human visual sense, a screen for each of the fields (F) 4 is stacked in layers thus enabling a natural image being free from a flicker to be obtained. Moreover, as shown in FIG. 7, by dividing one field period into a plurality of sub-fields (SF) and by changing a number of times of discharging during a sustaining period in each sub-field and by combining these sub-fields, gray-scale display can be achieved.
In FIG. 7, one field is made up of seven sub-fields and at a head of each sub-field a combined period 5 including a sustaining erasing period, a pre-discharging period, and a pre-discharging erasing period is provided and then a writing period 6 and a sustaining period 7 are set in order. By reducing frequency (the number of times) of discharging occurring during the sustaining period 7 by about fifty percent sequentially beginning at a leading sub-field, weights are assigned. According to this method, by selecting the above-described sub-field within one field to have sustaining discharging occur, emitting luminance can be controlled based on the number of times of the sustaining discharging in the selected sub-field, thus enabling gray-scale display to be achieved.
However, when the AC plasma display panel is driven by the conventional method described above, during a period from a start of operations (by power-ON) to a time (within one second) when supply power becomes stable, a level of a voltage pulse does not reach a predetermined value and timing is not yet calibrated. Therefore, the conventional method presents a problem in that erroneous discharge occurs by an influence of residual charges during the writing period or the sustaining period and then light is emitted during the sustaining period in the sub-field and continued emitting of light caused by the erroneous discharge is unfavorably conspicuous.